Solenoid valves have been widely used in medical devices such as massaging machines. U.S. Pat. No. 5,992,461 discloses a conventional solenoid valve including a valve body and an electromagnetic body. The valve body has two ports. The electromagnetic body includes a U-shaped magnetically conductive member, a coil bobbin defining an inner hole, a coil wound around the coil bobbin, a stator disposed in one end of the coil bobbin, and a hollow plunger disposed in the other end of the coil bobbin. The stator has a third port. The plunger includes therein a pair of plugs and an inner spring between the plugs. An outer spring is disposed between the plunger and the stator. When the coil is energized, the plunger is magnetized and attracted to the stator such that the plug at the end of the plunger closes the third port of the stator, and the two ports of the valve body communicate with each other. When the coil is not energized, the plunger is returned to its initial position by the restoring force of the outer spring so as to close the first port of the valve body, and the second port of the valve body communicates with the third port of the stator.
In the above solenoid valve, the stator and the U-shaped magnetically conductive member are in rigid contact with each other. When the plunger moves towards the stator under the influence of the magnetic force, a large impact occurs when the two components make contact generating vibrations and noise. The vibrations are easily transmitted to the coil bobbin and U-shaped magnetically conductive member, thus generating a high level of noise. This noise may be disturbing for users and patients.